In general, gaseous discharged lamps comprise a transparent or translucient glass envelope containing a gas or vapor in an otherwise evacuated enclosure which upon energization glows to provide an intense light. The vapor may be a metalic vapor such as that produced by a small amount of mercury in the evacuated enclosure. Thus, upon energization the mercury forms a vapor which is ionized to create an intense glow.
A common method of energization of the lamp is provided by using electrodes which extend into the enclosure. A potential connected across the ends of the electrodes external to the envelope effects the glow. Lamps of the type described find particular use in mask projection systems of the type disclosed in U.S. Pat. No. 4,011,011 having the same assignee as the present invention wherein photo resist-coated wafers are exposed to the light projection of a mask containing intricate circuit details in the production of integrated circuits. A lamp used in such an environment must be precisely positioned in the optical projection system. Thus, assuming an accurately positioned mounting arrangement the lamp itself must be dimensionally accurate in its configuration.
A lamp manufactured for use in the mask projection system described in the above mentioned patent is disclosed and claimed in the U.S. Pat. No. Re: 30,315 having the same assignee as the present application. This patent describes a lamp having a glass envelope defining a cavity of capillary cross-section and arcuate configuration. One end of the envelope has a metal mounting base fixed thereto whose configuration and relationship to the rest of the envelope is such that upon installation of the base in a mounting fixture the lamp is accurately positioned in its operating environment.
In the manufacture of the lamp, the metal base has an axial bore sufficiently large to receive an end stub of the envelope. The base and envelope are positioned axially, radially and angularly relative to each other with the aid of a jig. An epoxy is then inserted in the annular space defined the outside diameter of the stub and the inside diameter of the bore. The epoxy is allowed to harden and may be aided in the hardening process by heating.
Aside from the time consuming steps required to position and fix the metal base on the glass envelope the use of epoxy, although the best obtainable for firing glass to metal, results in 2-3% of the lamps being discarded due to loose bases.
Also, a defective batch of epoxy can result in the reworking of an entire day's production run.
It has been long felt that substitution of glass base for the metal base would overcome the above disadvantages of the metal base lamp. Since the glass base may be fused onto the envelope, it would eliminate problems associated with use of epoxy. Use of a glass base would lessen the problems of short circuiting since the glass base is insulating. In addition, use of a glass base results in a less costly manufacturing process for the lamp.